1. Field of the Invention
The invention relates to a tunable DFB-laser.
2. Description of Related Art
Single-wave (single-frequency) laser diodes which have continuously tunable wavelengths over a certain range (for example, 0.5-1nm given a 1.55um wavelength) are a preferred requirement for modern optical communications systems.
The manufacture of appropriate, single-wave laser diodes currently occurs almost exclusively using the principal of distributed feedback. These lasers are referred to as distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers. The tuning of the wavelength has been produced by modifying the refractive index in the region of the Bragg grating (or, respectively, of the Bragg wavelength). For this reason, the lasers are longitudinally divided into a plurality of sections and are provided with separate electrodes. A critical disadvantage of these configurations (as discussed, for example, in the article by C. Y. Kuo, N. K. Dutta, "Characteristics of Two-Electrode DFB Lasers", Electronic Letters 24, 947-949 (1988)) is caused by inhomogeneities or, respectively, discontinuities in the tuning (longitudinal mode change). This disadvantage can be avoided by additional application of a third section or, respectively, of a fourth electrode. However, the division of the currents into the three sections must occur within narrow limits that are located using an extremely involved measuring technique. This type of operation is extremely critical in practice and component aging can lead to mode changes since the division of the currents can unpredictably change after a few thousand operating hours.